In-situ chemical-mechanical planarization pad metrology using ultrasonic imaging

ABSTRACT

Chemical-mechanical planarization (CMP) apparatus and methods for detecting polishing pad properties using ultrasonic imaging is presented. An ultrasonic probe assembly transmits ultrasonic signals onto the surface of a polishing pad during a CMP process. Reflected ultrasonic signals are collected and analyzed to monitor polishing pad properties in real-time. This allows CMP process adjustments to be made during the CMP process.

BACKGROUND OF THE INVENTION

[0001] This invention relates to apparatus and methods ofchemical-mechanical planarization using ultrasonic imaging. Moreparticularly, this invention relates to a chemical-mechanicalplanarization pad metrology apparatus that transmits an ultrasonicsignal onto the surface of a polishing pad to monitor polishing padproperties in real-time.

[0002] Fabricating integrated circuit devices is a complex multi-stepprocess that creates structures with various electrical properties toform a connected set of devices. Multiple layers of conducting,semiconducting, dielectric, and insulting materials are deposited on asubstrate during integrated circuit device fabrication. As these devicesbecome smaller and more densely packed, more levels of photolithographyand additional processing steps are often required.

[0003] Often, imperfect substrate fabrication and imperfect integratedcircuit layer deposition result in formation of undesirable topography(e.g., recesses, protrusions, scratches, etc.) on the substrate and onone or more of the deposited layers. Because undesirable topography cancompromise the integrity of an integrated circuit device (e.g., atopographical recess in a dielectric layer can impose step coverageproblems for the deposition of another integrated circuit layer, andundesirable topology can cause depth of focus issues duringphotolithography), the substrate and each deposited layer of anintegrated circuit device are preferably planarized (i.e., made level)before additional layers of integrated circuit material are deposited.

[0004] A common technique used to planarize the surface material of anintegrated circuit wafer is chemical-mechanical planarization (“CMP”).Known CMP processes are used to remove undesirable topology from layersof integrated circuit material. The rotating polishing pad mechanicallypolishes (i.e., removes undesirable topography from) the surfacematerial of the integrated circuit wafer. Concurrently, a fluid-basedchemical (i.e., a chemical polishing “slurry”) is dispensed onto thesurface of the polishing pad to facilitate the removal of undesirabletopography. Chemical polishing slurry may react with the integratedcircuit material. That is, the slurry chemically weakens surfacematerial of the wafer so that the surface is more easily removed by themechanical abrasion of the polishing pad. Chemical polishing slurry mayalso be an inert liquid applied to the polishing pad. The inert liquidfacilitates the removal of mechanically-ground integrated circuitmaterial.

[0005] As device dimensions continue to scale down, CMP processes becomemore critical in the process flow. For example, polishing actions shouldbe performed such that scratches or other defects do not appear on thesurface of the polished integrated circuit wafer. Furthermore, in orderto achieve uniform planarity, a constant polishing rate should bemaintained. Thus, polishing pad maintenance plays a significant role indiminishing the drawbacks of the CMP process.

[0006] It has been shown that polishing pad properties, such as padroughness (or texture), pad groove depth (which determines pad wear andpad erosion), pad density, pad thickness, and elastic modulus, influenceCMP removal rates and uniform planarity. However, information thatrelates polishing pad properties to polishing performance is sparsebecause of inadequate measurement techniques.

[0007] Currently, surface topography measurements are obtained usingknown optical systems, such as a laser scanning microscope. However,there are significant drawbacks with the use of a laser scanningmicroscope. First, the CMP pad must be cleaned and dried before it canbe examined with the microscope, which is a time-consuming andinefficient process. Also, because scanning laser microscopes arecumbersome, the examination process is performed offline (i.e., outsideof the CMP tool), which is also a time-consuming and inefficientprocess. Furthermore, because CMP pads are typically semi-translucent,scanning laser microscopes and other known optical systems havedifficulty resolving scratches and polishing pad defects.

[0008] In view of the foregoing, it would be desirable to collectpolishing pad data and transmit the collected data in real-time to aprocessor such that process adjustments may be made during a CMPprocess.

[0009] It would also be desirable to maximize wafer throughput (i.e.,the number of wafers processed per unit of time) while determining andmonitoring polishing pad properties.

[0010] It would further be desirable to provide an apparatus for in-situCMP pad metrology that uses ultrasonic imaging.

SUMMARY OF THE INVENTION

[0011] It is an object of this invention to collect polishing pad dataand transmit the collected data in real-time to a processor such thatprocess adjustments may be made during a CMP process.

[0012] It is also an object of this invention to maximize waferthroughput while determining and monitoring polishing pad properties.

[0013] It is a further object of this invention to provide an apparatusfor in-situ CMP pad metrology that uses ultrasonic imaging.

[0014] In accordance with this invention, an apparatus and method forpolishing pad metrology using ultrasonic imaging is provided thatdetermines and monitors polishing pad properties and allows real-timeprocess adjustments to a CMP process.

[0015] In a preferred embodiment of the invention, ultrasonic imaging isperformed by an ultrasonic probe assembly, which preferably includes anultrasonic source and an ultrasonic detector. The ultrasonic probeassembly transmits ultrasonic signals onto the surface of a polishingpad. While some of the transmitted ultrasonic signals propagate throughthe polishing pad, other transmitted ultrasonic signals are reflectedfrom the surface of the polishing pad and are collected by theultrasonic detector. The reflected ultrasonic signals are analyzed inreal time to provide real-time monitoring of the polishing pad as itpolishes. For example, upon correlating the reflected ultrasonic signalswith polishing pad position data from which the measurement was taken,contour maps and cross-sectional pad profiles can be obtained. Also,real-time pad properties, such as pad wear and pad erosion can beobtained from the reflected ultrasonic signals.

[0016] In some embodiments, the data collected while monitoring thepolishing pad as it polishes may be transmitted to, for example,engineers, computer software, or apparatus that generates statisticalprocess control (SPC) charts. Based at least in part on the collecteddata, real-time process adjustments may be made. For example, theprocess recipe may be automatically adjusted to compensate for pad wearor pad erosion, thus extending the life of a polishing pad and improvingwafer throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects and advantages of the invention willbe apparent upon consideration of the following detailed description,taken in conjunction with the accompanying drawings, in which likereference characters refer to like parts throughout, and in which:

[0018]FIG. 1 is a schematic diagram of an embodiment of a CMP apparatusfor in-situ monitoring of polishing pad properties according to theinvention;

[0019]FIG. 2 is a flowchart of an embodiment of a method of monitoringpolishing pad properties and then adjusting a CMP process based on themonitored properties according to the invention;

[0020]FIG. 3 is a graph of time of flight of ultrasonic signals versuspolishing pad position for a polishing pad;

[0021]FIG. 4 is a graph of reflectivity versus polishing pad positionfor a polishing pad;

[0022]FIG. 5 is a reflection image of the surface of a polishing pad;

[0023]FIG. 6 is a time of flight surface profile image created fromcollected position data and time of flight data of a polishing pad;

[0024]FIG. 7 is a graph of time of flight of the ultrasonic signalsversus polishing pad position for a polishing pad immersed in deionizedwater;

[0025]FIG. 8 is a graph of reflectivity versus polishing pad positionfor a polishing pad immersed in deionized water;

[0026]FIG. 9 is a reflection image of the surface of a polishing padimmersed in deionized water; and

[0027]FIG. 10 is a time of flight surface profile image created usingcollected position data and time of flight data of a polishing padimmersed in deionized water.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The invention provides CMP pad metrology apparatus and methodsfor in-situ determination and monitoring of polishing pad propertiesusing ultrasonic imaging during a CMP process.

[0029] Ultrasonic imaging uses a focused ultrasonic signal transmittedonto the surface of a polishing pad. While ultrasonic imaging is widelyused in the medical industry (e.g., non-invasive imaging of a fetus) andin the aerospace industry (e.g., defect detection in structures),ultrasonic imaging can also be advantageously used in the semiconductorindustry for monitoring polishing pad properties during a CMP process.

[0030] Ultrasonic imaging differs from other well-known optical imagingmethods because it does not require sample preparation (e.g., polishingpads that are cleaned and dried) and because it provides anon-destructive method for determining physical properties,microstructure, and topography images. Ultrasonic probes are alsoportable and cost-effective. Even further, ultrasonic imaging can beapplied to all states of matter except plasma. For example, unlike knownoptical imaging methods, propagation of an ultrasonic signal through amaterial is not affected by the material's transparency or opacity.Because polishing pads are typically semi-transparent, known opticalimaging methods typically have difficulty resolving surface defects.

[0031] In accordance with the invention, apparatus and methods areprovided for polishing pad metrology using ultrasonic imaging thatdetermines and monitors polishing pad properties and allows real-timeprocess adjustments to a CMP process.

[0032]FIG. 1 illustrates an embodiment of CMP apparatus havingultrasonic imaging for in-situ monitoring of CMP pad properties inaccordance with the invention. CMP apparatus 100 has a platen 102 and apolishing pad 104. Platen 102 and polishing pad 104 are driven by adrive assembly 110 to move with translation motions 106 and rotationmotions 108. Polishing pad 104 may be a conventional polishing pad madefrom a relatively soft, thin, and porous material, such as polyurethane.Polishing pad 104 may also be an abrasive polishing pad with abrasiveparticles fixedly bonded to a suspension medium. CMP apparatus 100 mayalso have an underpad 109 attached to the surface of platen 102 forsupporting polishing pad 104.

[0033] To planarize a substrate 114, a conditioning head assembly 116presses substrate 114 against polishing pad 104 in the presence offluid-based polishing chemical 112. As used herein, “substrate” includesa base layer (e.g., a silicon wafer, a semiconductor material, or aninsulating material) and may include one or more integrated circuitlayers deposited on the base layer. Conditioning head assembly 116 maybe driven to move backwards and forwards by a conditioning arm 118.Platen 102 and conditioning head assembly 116 move relative to oneanother to translate substrate 114 across the surface of polishing pad104. As a result, the rotating polishing pad 104 mechanically polishes(i.e., removes undesirable topography from) the surface material ofsubstrate 114. Concurrently, a fluid-based polishing chemical 112 (i.e.,a chemical polishing “slurry”) is dispensed onto the surface ofpolishing pad 104. Chemical polishing slurry 112 may react with thesurface of substrate 114. In other embodiments, chemical polishingslurry 112 may be an inert liquid applied to the polishing pad tofacilitate the removal of undesirable topography. For example, deionizedwater applied to the interface between polishing pad 104 and substrate114 may facilitate removal of mechanically-ground integrated circuitmaterial.

[0034] CMP processes should consistently and accurately produce auniformly planar surface on the substrate in order to preciselyfabricate integrated circuit devices. However, polishing pad 104typically wears unevenly as it is used, thus affecting its removal rate.The removal rate of integrated circuit material varies based at least inpart on age and erosion (i.e., pad wear) of polishing pad 104. Forexample, polishing pad 104 may be substantially more worn at the centerof the pad than at the edge of the pad. Performing a CMP process on asubstrate with such a non-uniform polishing pad results in non-uniformlyplanarized substrates. Thus, polishing pad 104 is preferably“conditioned” as part of the CMP process in order to restore polishingpad 104 to its original removal rate. When polishing pad 104 can nolonger be conditioned, polishing pad 104 should be replaced.

[0035] As repeated CMP processes are performed, the properties ofpolishing pad 104 should be observed. Such properties may include, forexample, pad roughness (i.e., texture), pad groove depth (whichdetermines pad depth and pad erosion), pad density, pad thickness, andelastic modulus. To monitor and determine these polishing padproperties, CMP apparatus 100 also includes an ultrasonic probe assembly120 and a computer processor 124. Ultrasonic probe assembly 120preferably has a diameter between about 3 millimeters and 50millimeters. Processor 124 preferably has an image processing card 126and a data acquisition card 128.

[0036] Although a single ultrasonic probe assembly 120 is shown,multiple ultrasonic probe assemblies may be positioned within CMPapparatus 100 to facilitate monitoring of polishing pad properties.

[0037] In one embodiment, ultrasonic probe assembly 120 has aconventional “contact” ultrasonic transducer, where the interface mediumbetween polishing pad 104 and ultrasonic probe assembly 120 is asuitable liquid or liquid gel material. In an alternative embodiment,ultrasonic probe assembly 120 has a “non-contact” ultrasonic transducer,in which there is no interface medium (i.e., air/gas) between polishingpad 104 and ultrasonic probe assembly 120 (a vacuum exists).

[0038] Ultrasonic probe assembly 120 preferably includes an ultrasonicsource 130 and an ultrasonic detector 132 for transmitting and receivingultrasonic signals. Ultrasonic source 130 is configured to transmit anultrasonic signal at an area on the surface of polishing pad 104 assubstrate 114 is being polished. Note that transmitting and receivingultrasonic signals may also be performed between polishing steps (e.g.,between wafers or lots). Ultrasonic probe assembly 120 preferablycontacts chemical polishing slurry 112. While chemical polishing slurry112 may be any suitable slurry, chemical polishing slurry 112 ispreferably deionized water to provide an interface medium which iseasily controllable and repeatable (e.g., it can be maintained at aconstant temperature, has well-known properties, and is readilyavailable). Note that if ultrasonic probe assembly 120 has a“non-contact” ultrasonic transducer, ultrasonic probe assembly 120 isnot in contact with chemical polishing slurry 112.

[0039] As shown in FIG. 1, ultrasonic probe assembly 120 is preferablyfixed to conditioning arm 118. In other embodiments, ultrasonic probeassembly 120 may be fixed to other suitable structures within CMPapparatus 100, such as conditioning head assembly 116, a slurry arm (notshown), or an overhead fixed ring (not shown). Processor 124 may beconfigured to direct conditioning arm 118 to move backwards and forwardsover the surface of polishing pad 104 during the CMP process. Theadvantage of fixing ultrasonic probe assembly 120 to conditioning arm118 is that processor 124 can calculate the real-time position ofultrasonic probe assembly 120 based at least in part on the position ofconditioning arm 118. Furthermore, because conditioning arm 118 movesbackwards and forwards across the diameter of polishing pad 104, whichpreferably rotates at a constant velocity, processor 124 can determinereal-time polishing pad properties for a substantial portion ofpolishing pad 104.

[0040] If desired, CMP apparatus 100 may include sensors (not shown) toobtain position data of ultrasonic probe assembly 120. The sensors maybe fixed to conditioning arm 118 or another suitable structure. Thesensors transmit position data to processor 124. In response toreceiving position data from the sensors, processor 124 correlates thecollected position data with the collected ultrasonic signals.

[0041] Ultrasonic source 130 transmits ultrasonic signals onto thesurface of polishing pad 104. Some ultrasonic signals may be absorbed(e.g., into chemical polishing slurry 112). Some ultrasonic signals maypropagate through polishing pad 104 and be subsequently reflected fromplaten 102. (Platen 102 is preferably a metal, such as aluminum, whichis an excellent reflector of ultrasonic signals). Some ultrasonicsignals may reflect off of polishing pad 104. In response to ultrasonicdetector 132 receiving reflected ultrasonic signals, ultrasonic probeassembly 120 transmits the reflected ultrasonic signals to an ultrasonicamplifier 122, which amplifies the signals before processing. Theamplified reflected ultrasonic signals are then transmitted to processor124 to determine the polishing pad properties for a particular positionon polishing pad 104.

[0042]FIG. 2 shows an illustrative method 200 for determining andmonitoring the properties of polishing pad 104 using ultrasonic probeassembly 120. At step 202, a user selects a process “recipe” usingcomputer processor 124 or other suitable processor that can control CMPapparatus 100. As used herein, a process recipe includes a set ofpolishing parameters that can be varied to achieve control of the CMPprocess. Such a process recipe may be, for example, a polish recipe, aconditioning recipe, or any other suitable recipe. Process parametersmay include, for example, the downward force applied by conditioninghead assembly 116, the duration of the polishing operation performed byconditioning head assembly 116, the amount of backforce pressure used tosecure substrate 114 to conditioning head assembly 116, the rotationalvelocity of conditioning head assembly 116, the oscillation ofconditioning head assembly 116, or any other appropriate processparameters. In other embodiments, the user may manually create acustomized process recipe. For example, the user may create a polishingrecipe by inputting desired process parameters into processor 124.

[0043] In response to selecting or inputting a process recipe, substrate114 is loaded onto CMP apparatus 100 at step 204. In some embodiments,CMP apparatus 100 may include a loading/unloading assembly (not shown).A cassette, holding at least one substrate, may be placed at theloading/unloading assembly. In response to CMP apparatus 100 detectingthe presence of a cassette at the loading/unloading assembly, CMPapparatus 100 transfers substrate 114 from the cassette to conditioninghead assembly 116 using a robot, a wafer transport arm, or othersuitable wafer carrier.

[0044] At step 206, the CMP process begins. In particular, conditioninghead assembly 116 holding substrate 114 is driven backwards and forwardsover the surface of polishing pad 104. As a result, the rotatingpolishing pad 104 mechanically polishes the surface material ofsubstrate 114. Concurrently, the chemical polishing slurry 112 isdispensed onto the surface of polishing pad 104.

[0045] While the CMP process is being performed (i.e., in-situ),ultrasonic source 130 transmits ultrasonic signals onto the surface ofpolishing pad 104 at step 208. In other embodiments, ultrasonic source130 transmits ultrasonic signals onto the surface of polishing pad 104after substrate 114 is polished (e.g., ex-situ). Some transmittedultrasonic signals may be reflected from polishing pad 104, while othersmay propagate through polishing pad 104 and be subsequently reflectedfrom platen 102. Ultrasonic detector 132 receives reflected ultrasonicsignals at step 210. At step 212, the reflected ultrasonic signals areamplified by ultrasonic amplifier 122. The amplified signals are thentransmitted to computer processor 124.

[0046] As computer processor 124 receives real-time reflected andamplified ultrasonic signals, computer processor 124 monitors theproperties of polishing pad 104 at step 214. At substep 216, processor124 determines real-time pad properties based at least in part on thereflected and amplified ultrasonic signals. For example, in response toreceiving ultrasonic signals reflected from polishing pad 104 andultrasonic signals reflected from platen 102, processor 124 maycalculate the thickness of polishing pad 104. As shown in FIGS. 3-10,processor 124 may generate ultrasonic images and various graphs based atleast in part on the collected ultrasonic signals.

[0047] As shown in FIGS. 3-10, ultrasonic probe assembly 120 preferablyhas the capability of resolving at least micron-sized polishing padfeatures, thus allowing processor 124 to measure pad properties, such aspad roughness (or texture), pad groove depth, and other physical padproperties.

[0048]FIG. 3 shows the measured round-trip travel time (i.e., time offlight) of ultrasonic signals for a polishing pad versus position for anon-contact ultrasonic signal transmitted over 50 millimeters of thepolishing pad. From the graph shown, processor 124 can determine thethickness of the polishing pad and pad groove depth. Processor 124 canalso create a cross-sectional profile of the polishing pad.

[0049]FIG. 4 shows a graph of reflectivity versus position for anon-contact ultrasonic signal transmitted over 50 millimeters of thepolishing pad. Reflectivity is determined by calculating the areaunderneath a particular transmission or reflected peak. In FIG. 4, thehigher the reflectivity, the smoother the surface. Thus, FIG. 4illustrates the surface roughness of the polishing pad.

[0050]FIGS. 5 and 6 show a reflection image and a time of flightsurface-profile image generated using position data and time of flightmeasurements. At a position along the scan, processor 124 estimates thedepth of any feature that reflects the ultrasonic signal based at leastin part on the time of flight of the ultrasonic signal. The ultrasonicdetector operates with a time gate chosen so that its output indicatesthe amplitude of the ultrasonic signal reflected from the polishing padat that particular position. Once the scan has been completed, processor124 processes the position data and the associated depth and amplitudedata into a single three-dimensional graph that shows both depth andamplitude as functions of position. In particular, FIGS. 5 and 6 providea real-time topography image of the polishing pad.

[0051] Note that while FIGS. 3-6 were performed using a non-contacttransducer (i.e., no interface medium), the ultrasonic probe assemblymay also resolve polishing pad features while the polishing pad isimmersed in an interface medium. For example, FIGS. 7-10 show a time offlight versus position graph, a reflectivity versus position graph, areflection image, and a time of flight surface profile image,respectively, for a polishing pad immersed in deionized water.

[0052] Returning to FIG. 2, in response to processor 124 monitoring theproperties of polishing pad 104, processor 124 may automatically adjustthe process recipe (selected at step 202) based at least in part on thedetermined real-time pad properties. Automatically adjusting the processrecipe improves throughput while optimizing polishing parameters. Forexample, processor 124 may automatically adjust the downward polishforce or other polishing parameters to compensate for pad wear.Processor 124 may also notify the user when polishing pad 104 requireschanging (e.g., based on pad wear monitoring).

[0053] The determined real-time pad properties (e.g., surface topographymaps, pad thickness measurements, etc.) may also or instead betransmitted to the user. Alternatively, statistical process control(SPC) charts may be generated based on the pad properties. The user canthen manually adjust the process recipe.

[0054] Although the invention is described herein in terms ofchemical-mechanical planarization, the invention is also applicable tomechanical planarization of substrates.

[0055] Thus it is seen that ultrasonic signals may be used with CMPapparatus to determine and monitor polishing pad properties and toprovide real-time process control. One skilled in the art willappreciate that the invention can be practiced by other than thedescribed embodiments, which are presented for purposes of illustrationand not of limitation, and the invention is limited only by the claimswhich follow.

I claim:
 1. A method of monitoring chemical-mechanical polishing pads, the method comprising: transmitting ultrasonic signals onto the surface of a polishing pad, wherein a portion of the ultrasonic signals are reflected; detecting the reflected ultrasonic signals; and processing the reflected ultrasonic signals to monitor the polishing pad.
 2. The method of claim 1 wherein the processing comprises determining physical properties of the polishing pad based at least in part on the reflected ultrasonic signals.
 3. The method of claim 1 wherein the processing comprises generating a surface topography image of the polishing pad based at least in part on the reflected ultrasonic signals.
 4. The method of claim 1 further comprising automatically adjusting a chemical-mechanical planarization process recipe based at least in part on the processed reflected ultrasonic signals.
 5. The method of claim 1 further comprising receiving manually entered adjustments to a process recipe during a chemical-mechanical planarization process after the reflected ultrasonic signals are processed.
 6. A method of monitoring chemical-mechanical polishing pads, the method comprising: receiving a chemical-mechanical planarization process recipe; polishing a substrate with a polishing pad based on the received process recipe; transmitting ultrasonic signals onto the surface of the polishing pad while simultaneously polishing the substrate, wherein a portion of the ultrasonic signals are reflected; collecting the reflected ultrasonic signals; processing the reflected ultrasonic signals to determine physical properties of the polishing pad; and adjusting the process recipe based at least in part on the determined physical properties of the polishing pad.
 7. The method of claim 6 wherein the process recipe is a polishing recipe.
 8. The method of claim 6 wherein the process recipe is a conditioning recipe.
 9. The method of claim 6 wherein the processing comprises generating a surface topography image of the polishing pad based at least in part on the reflected ultrasonic signals.
 10. The method of claim 6 wherein the adjusting comprises using a computer processor to automatically adjust the process recipe based at least in part on the determined physical properties of the polishing pad.
 11. The method of claim 6 wherein the adjusting comprises receiving manually entered adjustments.
 12. The method of claim 6 wherein the physical properties of the polishing pad are selected from the group consisting of pad roughness, pad groove depth, pad wear, pad erosion, pad density, pad thickness, elastic modulus of the polishing pad, and any combination thereof.
 13. The method of claim 6 further comprising issuing a notification when the polishing pad requires replacement.
 14. A method of monitoring chemical-mechanical polishing pads, the method comprising: receiving a chemical-mechanical planarization process recipe; polishing a substrate with a polishing pad based on the received process recipe; transmitting ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected; collecting position data for each transmitted ultrasonic signal substantially simultaneously while transmitting the ultrasonic signals; collecting the reflected ultrasonic signals; correlating the collected position data with the reflected ultrasonic signals; and generating surface topography images using the collected position data and the reflected ultrasonic signals.
 15. A method of monitoring chemical-mechanical polishing pads, the method comprising: receiving a chemical-mechanical planarization process recipe selected by a user; polishing a substrate with a polishing pad based on the selected process recipe; immersing the substrate and polishing pad in deionized water; transmitting ultrasonic signals onto the surface of the polishing pad simultaneously while polishing, wherein a portion of the ultrasonic signals are reflected; detecting the reflected ultrasonic signals; processing the reflected ultrasonic signals to determine physical properties of the polishing pad; and adjusting the process recipe based at least in part on the determined physical properties of the polishing pad.
 16. The method of claim 15 wherein the adjusting comprises allowing a user to enter adjustments to the process recipe.
 17. The method of claim 15 wherein the adjusting comprises using a computer processor to automatically adjust the process recipe based at least in part on the determined physical properties of the polishing pad.
 18. The method of claim 15 wherein the process recipe is a polishing recipe.
 19. The method of claim 15 wherein the process recipe is a conditioning recipe.
 20. The method of claim 15 wherein the processing comprises generating a surface topography image of the polishing pad.
 21. The method of claim 15 wherein the processing comprises generating a statistical process control chart.
 22. The method of claim 15 wherein the physical properties of the polishing pad are selected from the group consisting of pad roughness, pad groove depth, pad wear, pad erosion, pad density, pad thickness, elastic modulus of the polishing pad, and any combination thereof.
 23. A method of monitoring chemical-mechanical polishing pads, the method comprising: receiving a chemical-mechanical planarization process recipe; polishing a substrate with a polishing pad based on the selected process recipe; transmitting ultrasonic signals onto the surface of the polishing pad simultaneously while polishing, wherein a portion of the ultrasonic signals are reflected; detecting the reflected ultrasonic signals; processing the reflected ultrasonic signals to determine physical properties of the polishing pad; and receiving adjustments to the process recipe during the polishing.
 24. The method of claim 23 wherein the processing comprises generating a surface topography image of the polishing pad.
 25. The method of claim 23 wherein the processing comprises generating a statistical process control chart.
 26. The method of claim 23 wherein the physical properties of the polishing pad are selected from the group consisting of pad roughness, pad groove depth, pad wear, pad erosion, pad density, pad thickness, elastic modulus of the polishing pad, and any combination thereof.
 27. A chemical-mechanical planarization apparatus for monitoring chemical-mechanical polishing pads, the apparatus comprising: means for receiving a chemical-mechanical planarization process recipe; means for polishing a substrate with a polishing pad based on the process recipe; means for transmitting ultrasonic signals onto the surface of the polishing pad while simultaneously polishing the substrate, wherein a portion of the ultrasonic signals are reflected; means for collecting the reflected ultrasonic signals; means for processing the reflected ultrasonic signals to determine physical properties of the polishing pad; and means for adjusting the process recipe based at least in part on the determined physical properties of the polishing pad.
 28. A chemical-mechanical planarization apparatus for monitoring chemical-mechanical polishing pads, the apparatus comprising: means for receiving a chemical-mechanical planarization process recipe selected by a user; means for polishing a substrate with a polishing pad based on the selected process recipe; means for transmitting ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected; means for collecting position data for each transmitted ultrasonic signal substantially simultaneously while transmitting the ultrasonic signals; means for collecting the reflected ultrasonic signals; means for correlating the collected position data with the reflected ultrasonic signals; and means for generating a surface topography image using the collected position data and the reflected ultrasonic signals.
 29. Planarization apparatus configured to monitor a polishing pad while polishing a substrate, the apparatus comprising: support means; assembly means movably coupled to the support means for moving a substrate; ultrasonic means fixed to the support means for transmitting ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected, and for receiving the reflected ultrasonic signals; amplifier means for amplifying the received reflected ultrasonic signals; and computer means to determine real-time polishing pad properties based on the reflected ultrasonic signals.
 30. A chemical-mechanical planarization apparatus configured to monitor a polishing pad while polishing a substrate, the apparatus comprising: an arm; a head assembly movably coupled to the arm; an ultrasonic probe assembly fixed to the arm and having an ultrasonic source and an ultrasonic detector, wherein: the ultrasonic source is configured to transmit ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected; and the ultrasonic detector is configured to receive the reflected ultrasonic signals; an ultrasonic amplifier that amplifies the reflected ultrasonic signals received by the ultrasonic detector; and a computer processor configured to determine real-time polishing pad properties based on the reflected ultrasonic signals.
 31. The chemical-mechanical planarization apparatus of claim 30 wherein the processor is further configured to generate a surface topography image of the polishing pad based at least in part on the determined real-time polishing pad properties.
 32. The chemical-mechanical planarization apparatus of claim 30 wherein the processor is further configured to adjust a process recipe based at least in part on the determined real-time polishing pad properties.
 33. The chemical-mechanical planarization apparatus of claim 32 wherein the process recipe is a polishing recipe.
 34. The chemical-mechanical planarization apparatus of claim 32 wherein the process recipe is a conditioning recipe.
 35. The chemical-mechanical planarization apparatus of claim 30 wherein the processor is further configured to issue a notification indicating that the polishing pad requires changing based at least in part on the determined real-time polishing pad properties.
 36. A chemical-mechanical planarization apparatus configured to monitor a polishing pad while polishing a substrate, the apparatus comprising: an arm; a head assembly movably coupled to the arm; an ultrasonic probe assembly fixed to the arm and having an ultrasonic source and an ultrasonic detector, wherein: the ultrasonic source is configured to transmit ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected; and the ultrasonic detector is configured to receive the reflected ultrasonic signals; an ultrasonic amplifier that amplifies the reflected ultrasonic signals received by the ultrasonic detector; and a computer processor configured to: determine real-time polishing pad properties based on the reflected ultrasonic signals; generate a surface topography image of the polishing pad based at least in part on the determined real-time polishing pad properties; and adjust a process recipe based at least in part on the determined real-time polishing pad properties and the surface topography image.
 37. The chemical-mechanical planarization apparatus of claim 36 wherein the process recipe is a polishing recipe.
 38. The chemical-mechanical planarization apparatus of claim 36 wherein the process recipe is a conditioning recipe.
 39. A method of monitoring substrate polishing pads, the method comprising: transmitting ultrasonic signals onto the surface of a polishing pad, wherein a portion of the ultrasonic signals are reflected; detecting the reflected ultrasonic signals; and processing the reflected ultrasonic signals to monitor the polishing pad.
 40. A method of monitoring substrate polishing pads, the method comprising: receiving a process recipe; polishing a substrate with a polishing pad based on the received process recipe; transmitting ultrasonic signals onto the surface of the polishing pad while simultaneously polishing the substrate, wherein a portion of the ultrasonic signals are reflected; collecting the reflected ultrasonic signals; processing the reflected ultrasonic signals to determine physical properties of the polishing pad; and adjusting the process recipe based at least in part on the determined physical properties of the polishing pad.
 41. An apparatus configured to monitor a polishing pad while polishing a substrate, the apparatus comprising: an arm; a head assembly movably coupled to the arm; an ultrasonic probe assembly fixed to the arm and having an ultrasonic source and an ultrasonic detector, wherein: the ultrasonic source is configured to transmit ultrasonic signals onto the surface of the polishing pad, wherein a portion of the ultrasonic signals are reflected; and the ultrasonic detector is configured to receive the reflected ultrasonic signals; an ultrasonic amplifier that amplifies the reflected ultrasonic signals received by the ultrasonic detector; and a computer processor configured to determine real-time polishing pad properties based on the reflected ultrasonic signals. 